Flash custom recovery, to do it hold Power+Volume UP Afaik.
Connect your phone to your PC, wait till it installs drivers. If it fails, install drivers from manufacturer website.
Download a flash tool for HTC one. I really, never had a HTC so I can't help you here.
Download appropriate TWRP Recovery img for your phone (Google it)
Insert it into your desired flash application and flash it.
(But before you do that, unlock bootloader if it's locked)
It should reboot into TWRP Recovery. Boot your phone like everyday but this time, download those "Root" .zips. They're available everywhere and i bet it's probably on XDAForums.
Then turn off your phone, and now boot into recovery holding Power+Volume Down
Head to Flash tab and flash your .zip. Reboot your phone into system and viola, SuperSU.

Flash custom recovery, to do it hold Power+Volume UP Afaik.
Connect your phone to your PC, wait till it installs drivers. If it fails, install drivers from manufacturer website.
Download a flash tool for HTC one. I really, never had a HTC so I can't help you here.
Download appropriate TWRP Recovery img for your phone (Google it)
Insert it into your desired flash application and flash it.
It should reboot into TWRP Recovery. Boot your phone like everyday but this time, download those "Root" .zips. They're available everywhere and i bet it's probably on XDAForums.
Then turn off your phone, and now boot into recovery holding Power+Volume Down
Head to Flash tab and flash your .zip. Reboot your phone into system and viola, SuperSU.

Click to expand...

You forgot about something, you have to unlock the bootloader to be able to Flash a Custom Recovery...